1. Field of the Invention
The present invention relates to an image forming apparatus of a so-called tandem system and a method thereof. Particularly, the invention relates to an apparatus wherein exposure units are each provided in correspondence to each latent image carrier, the exposure unit using, as a deflector, an oscillation mirror in resonant oscillations for optical scanning.
2. Description of the Related Art
As the image forming apparatus of this type, a so-called tandem image forming apparatus has conventionally been known wherein photosensitive members, exposure units and developing units are each dedicated to each of mutually different four color components including, for example, yellow, magenta, cyan and black. In this tandem apparatus, an image of each color component is formed on the photosensitive member in the following manner. A light source of one exposure unit for one color component is controlled based on image data indicative of an image of the color component, while a light beam from the light source is scanned by means of the deflector of the exposure unit thereby forming, on the photosensitive member, a latent image corresponding to the image data related to the color component. Subsequently, the resultant latent images are developed with toners of mutually different colors to form toner images of plural colors. Then, the toner images of the plural colors are superimposed on each other on a transfer medium to form a color image thereon.
Aiming at downsizing and speeding up the deflector, it has heretofore been proposed to employ a resonant oscillation mirror as the deflector, the oscillation mirror disclosed in, for example, Japanese Unexamined Patent Publication No. 1-302317, page 2 and FIG. 2 to FIG. 4. In this apparatus, the oscillation mirror is driven into resonant oscillations by matching a frequency of a drive signal applied to the oscillation mirror with a natural resonant frequency of the oscillation mirror, whereby a relatively great amplitude is attained. The light beam from the light source is guided to the oscillation mirror in resonant oscillations so as to scan the light beam.